Calculates physiological dead-space fraction using arterial and mixed-expired carbon dioxide.
Overview
Calculates physiological dead-space fraction using arterial and mixed-expired carbon dioxide.
Clinical Significance
Represents the fraction of tidal volume not participating in carbon dioxide elimination when true mixed-expired CO₂ is used.
How It Is Calculated
- VD/VT = (PaCO₂ − PECO₂) / PaCO₂.
Interpretation
- Represents the fraction of tidal volume not participating in carbon dioxide elimination when true mixed-expired CO₂ is used.
Worked Example
Enter a clinically consistent set of values in the displayed units. MedicalC applies: VD/VT = (PaCO₂ − PECO₂) / PaCO₂.
Limitations
- This tool does not establish a diagnosis or mandate treatment.
- Published cut-offs may vary between cohorts and measurement methods.
- Calculation precision cannot compensate for poor source data.
Clinical Pearls
- Trend the result over time where clinically appropriate.
- Record the source values and units alongside the calculated result.
Common Mistakes
- Using the wrong unit.
- Combining measurements obtained at different times.
- Applying a research-derived threshold as a universal treatment trigger.
Frequently Asked Questions
What does this calculator provide?
Calculates physiological dead-space fraction using arterial and mixed-expired carbon dioxide.
Can this result be used alone?
No. It must be interpreted with clinical context and appropriate investigations.
What equation is used?
VD/VT = (PaCO₂ − PECO₂) / PaCO₂.
What is the main limitation?
The result depends on valid inputs and may not be calibrated for every population or setting.
References
- Bohr C. Ueber die Lungenathmung. Skand Arch Physiol. 1891. — Formula, physiological or validation reference.
Reviewed by: MedicalC Clinical Editorial Team
Last reviewed: July 2026